When you click on an individual reply and you want to reply to that user, you currently just create a reply starting with @username.
On top of that I'd like for the forum to also keep track of the topic you replied to and give people the option to click open the conversation:
This is an example topic with a couple of replies:
CONTENTS: I'm new here so I decided to make a topic
META: This post has 1 reply in Post Z, click to view that reply.
CONTENTS: I'm not a reply to any previous post in this topic, I'm a general reply to the topic.
CONTENTS: @A Hey!
META: This post is in direct reply to Post X, click to view post X
This feature is something I was looking forward to implementing when I decided to add reply buttons to every single post (was totally redundant for all of 6 months until @baris added the auto-quote)
If we can add a field where we keep track of who replied to what, this would be very neat. It would be up to the theme to decide whether or not to display this info though (unfortunately a lot of examples I've seen feel very cluttered)